Mercurial barometer



Aug- 17, 1943 J. B, E1IERSON 2,326,797

MERCURIAL BAROMETER Original Filed April 30, 1928 FICHE? FIGA Frql JOHN E). PETERSON `practically zero.

4Oneobject oftlfiis invention is to'prqv e; an -accurate instrument which will incl icz i tj, A 'altimeter setting pressuredirectly, witho1 lt the Ynecessity'of applying corrections. It vis believed i Patented Aug. 17, 1943 .MERCURIAL Sammies- John areterson; Bethesda, Ma f lippiication 23, V1321i),:Sfexia1- j amendedApril30,v 1928; "370 0. G 7 5 7) This invention relatesA Vto improvements -in' -mercurial barometer s,zand more particularly to the temperature conlpensation V of mercurial barometersv f x An object of the inventionis to prOVide means Y for freeing mercurial barometers of temperature errors and Vfor improving their"relijabi1ity, n especially under varying temperature conditions.

f It has been foundgthati the volume-oi the v .spaceabove the mercury in the tube of aimer- ,-pcurial barometer and the ygas pressure inthis space are properly proportonedth e temperature error of `the instrument can be reducedto that an -instrumentof this kind willbefatime saver, and will materially reduce the errors vin altimeter setting pressures. It has long been known to the art that alleroid Y barometersmayybe compensated for-temperature by leavingsome residual gasin the vacuum box, and that mercury barometers 'mail he kQ Olfl* pensated for "tf-initierture 'by'leavingr some residual gas inthe top of the tube above the mer- 1 cury.; However, this compensation until nowhas been imperfect inthat,it was,effective-atom one preferred pressure. A, The object of tlii'sffi'n-V tiomng the volume of the space abovetllcfmr* cury inthe tube and theggas pressure'inthis space, andhy taperingthemercury ciste r n'.`j`

With the foregoing and vother objectsin view,

the invention consists in the construction,com y f bination and arrangementof parts hereinafter described.` and'. illustrated in the drawing',.in which: w Fig. 1 shows an instrument with gas compensation for temperature variations anduwitn means for measuring and adjusting the 'pres sure of the compensating gas; l

Fig. 2 showsv a simpler formjof thevinstru-i.

ment wherein the cisterns of these instruments are tapered so as tomake a uniformlyspaced .pressure scale; v shows an instrument in which3 the Fig. s compensating, chamber is placed` adjacent to vthe mercury column-so as to assure Ythat they will be at the same temperature; and I Fig'. 4.. kshowsia vtwo.; liquideinstrumentghavmg ly without the ius'e of ai Vernier.; 1'

lIn all of these figures, l is the cisternlflis a nipple connection .tozthepressurewhich :is to be `V@measured,1 3 is thetubefltisa pressure scale, 5 is angaltitude scale/. -and .6; is the compensating f The :requirement for. temperatureecompensa- 207A I n v v 4 i Y A vWhere L; thecompensatingpressure Vention is to make available a mercurybarogneter which is perfectly compensated overwide A ranges of pressure andtemperatura; This com Y .pensation is accomplished byu properly propore,

tion 'may be expressedin theorm off equations. .i For temperature'. :compensation: by t'hs method .f it is necessary that the satised 4 atfzsome l" :instrumentl 'scale:

oint .near .the yj centerjgof; the.

`n=the linear coefficient of lexpansion of the V scale, cisternjff-material 'and the glass vin To avoid complications these the tube.

A coeicients havebeen assumed tube-equal. V :the Volume'of the Acorriiensating*space. Q y `lP the ratelofl change of pressure nddation'with temperature for" h metric;

the rate o fchan annata' angie u (eteg 't L YThe .compensating pre tothe inside area. bf uie'tube 'i' een multiplied bythe- Pressure P following":equations be pensated Y'barot v thefcpmpensating.

' pher'elbyiap mation Y n curi/itc: rise inftubes'` 8 Aand H, theproper--amount oflcompensatinglgaswlllbejtrapped. l-The'pres- Y "70 the pressure scale, the values of p for other readings on the pressure scale will be only approximately proportional to which would be the condition for yperfect compensation@ The econsequencesrof rthisgcdiscrepancy are (v1').':A av non-.uniform :pressure ,scale 'and (2) imperfect temperature compensation. The

y pressure scale maybe made uniform by theuse of a tapered cistern or a taperedtuba ^Ho.W-'

Y perature compensation canbe zsl-i'owrito;;cause Y only negligible errors. '.Ical error of la cba'rometer havingarrangeA-of 24 '..t0. 32;inches of mercury. .caused by :,ftemperature The maximum theoretikThe'possibility comprovidingmeansi Vcineas- .uring :the .l .compensating i' pressure and adjusting Vf: itiftothetproperi'vahlenhasibeenconsered and these means are incorporated in theiinstru- .fment shown `in 5Eig.:;l ,The compensating Volnume, compensating pressure-.and lcistern taper I,are calculated :for :.thisriinstrument, )by -the method VWhich;has already "beenj -described. After ;.tne manufacturer has fplaced: the :various .reference marks, in their proper glocations, this instrument can be shipped empty and llled with mercuryat'its idestination r Or if the mercury I f gets dirty; Qthe instrument; canfbe emptied for cleaning, relled and-adjusted for proper opera- -i tion, Without referencef to other standards.

To do this-the proper amount of mercury is;

poured intot'he cistern, andy a P/T factor is calculated by "dividing Vthe'-g{exlisting Latmos'plieric pressure fry. "the 19cm. temperature @absolute temperature). 1f .the L.atmospheric ,,preressure is fthe; roluief-.Qflthe 'lcmpe'satir gas at 'com temperature 5T, and room pressure evolume of l.the lcompensating Agas .fat lstandard values of :pressure-and temperature PM and TM. scale 11 replaced sothat the volume-@fstab s'frpnr'juncuon-sfto their/reactor sauger-,mms equation 'for vany values of atmospheric pressure andgrocni temperature.

surelat '2is then released "and the -mercu'ry'in the imam tube k"fans irqftne proper l readingV en Scalea N f These instructions 'presume that'tneiatmos- Q pheric "pressure is known approximately' before the barometer has been putinto operation. If

this pressure cannot be obtained, even approximately, PM (29 inches of mercury) may be used to calculate the P/T factor. An error in this assumed pressure will cause approximately l/20 of that error in the barometer indication. If

necessary the adjustment should be repeated' each time with amore accurate P /T factor until rthefresidualferror hasbeencreducejdito a satis- .ftactoryavalue- If desired, an inert gas or a gas with a higher lheat conductivity than air may be introduced into, the ,compensating chamber In any event V'there'should be no waterrvapor in the compen- :satingigas The presencecf water vapor can be ,avoided byperforming the filling operations at an Velevated"temperatureV and. by the use of drygingagents.

If it.,is desired to check the compensating y v; pressure y'Without opening the compensation 5 'chamber to the atmosphere and riskingrthe in- 'i troduction of -4moisture'vapor'thismay be ldone. ThefP/T' f'actor-is'acalculatedvand-"pressureisLapcolumn to this P/T factor. The mei'cuiyf-:inttube i8 '1 Willlnow haveiallenL to 44the I vicinityl of refer- -enceillimits |`2 Iand i3'. The air=r pressli'rei inf-tube H1-is adjusted tobringth'e :mercuryliitube i I I f to i' the rference markthereon. l'NOW the-pressure vin the tube 8 is slightly greater than-atmos- -'I2 3 have Ybeen :so plaoeilthat if1tliermercuryn v ft-ubc tifstan'cls between them,' tlfie`r'ror impr-essure 'indication will not-excee'd,sa'yplus olf-minus fenomeen 'w1 2 Y The compensating chambers'lof @israel-instru- 'vfgm'e'nts shown i-n Figsfl Aand C4 are l'lplaoeki in proximity to themercurybfcolum:n, so-'that if --there f -is -a temperature "gradie'ntarou'nditlie ibarometer, the compensationwill-istillibel-effective.

,49 iForl'prop'er#compensation f when l temperature qsulating the compensating char-fiber 'wand Athe 4setti-nglthe^airplane alt/imeter. Whemprepara- Y 2 tory to ila'niing, -tle r`pressure#scale of'- the sensi- "tivecaltimeterlisset'ttothisigure, -it--Will 'upon jl'andi'ng indicate i'the ealtitude'- of the "celdl-above 55rsea llevel, --previded there are --n'o errors in the furnished altimeter `v`setting l:pressurefor iin lt-he -a'ltin'iete'rl in making l a'lblind i ending itne fpilot reliesA on the f altimeter, #in this method to f determine ii'fris altitude-"above tithe Clanding ield 6^-until A-contaeiiwidthi ther *landing fbeami'is f made.

f' The v`altirneter setti-ng -:is etermi'ned 'by :Fredd- 'ing 4a frnercury' barometer', #making various: oorrecticns to'determine the true barometificzpres- "sureandffina'lly taking lthicriait-imatersettingr cor- 65 responding to the`lbarometric pressure .fffrom4 a v-table Aconstruci'led especllylfor the I,airport sat l 'Which'it isto bel'used,- l Y l `A preferred foi-*m (3f-temperature compensatledili-quid barometeriforuse asianL-.altimeterssetting instrument -is #shown :schematically in ='Fig. V3. Temperature compensation -siprovided :by lgas-inthe'eon'ipensation chamber i6, connected "-to the space; aboveythe rmercury, 'foeproyire a l'uniformaltirneter@setting scaleLL-thefcistern l istapered.

phe'ricL pressure J'and-the referenceJ marksk F2 and- Other'modicetions eind changes in thenumi made,V

ber and arrangement of the parts may be by those skilled in the art Without departing from thev nature of ,the invention, within the scope of what is hereinafter claimed. Y

The invention describedhereinmaybe manu iactui'edV rnd/or used by or for the Government of the United States of AmericaJ for governmen-v tal purposes Without the payment of any royal-V ties thereon or therefor. Y

Having thus set forth Vamd disclosed the neture of this invention what is claimed. is:

A liquid barometer comprising a tapered cis tern, a tube, liquid in said cistern extending -into said tube and Vspaced from the top thereof, said cistern having an openingtherein in ,com-

saidV opening beingglocatedfa'bove the liquidin tnecistern; the space above said liquid in Asalidr tube providing a, temperature compensation* chamber'the volume of Which-is approximately equalto the l.Volume corresponding to the height -cf the liquid column above themeni'scus of the f` i cistei'n multiplied by the hoi'zontalaea of the liquid in the reading section of the tube, a. comv ij pensating ges ,in said compression chamber; the expansion and contraction of which oompensates the instrument against changes vin temperature, theta-peifof said cisternbeing sof` proportion-edjthat thej/meniscus off the liquid munication with the pressure to bemeasure'd. ,i

column moves equal distances with unit4 varia- .Y

tions in the pressure.

-YLOHNl B. PETERSON.' l 

